In recent years, machining lasers such as semiconductor excitation solid-state lasers and fiber lasers achieve higher power. Consequently, conventional CO2 lasers and YAG lasers are replaced by these semiconductor excitation solid-state lasers and fiber lasers in machining fields of welding, cutting, and marking metal where the CO2 lasers and the YAG lasers have been typically employed. A laser diode (hereinafter, referred to as “LD”) is usually employed as a source of oscillating semiconductor excitation lasers. A large number of LDs arranged in serial or parallel in laser machining machines simultaneously emit light for the purpose of achieving higher power. Such an LD array is electrically configured by serially connecting LDs or connecting LD serial circuits in parallel, thus requiring large drive current as a whole.
In addition, the LD is a current driven element, and thus is typically configured as a constant current source circuit, that supplies drive current required to oscillate lasers with desired power as constant current. Such a highly-efficient constant current source circuit employing a switched-mode power supply system typically uses reactors, and thus, if short width laser pulses are to be outputted according to machining conditions, the output current has a low response speed, and cannot be a rectangular wave.
A drive circuit is devised in which a switching device is arranged in parallel to LDs, and is turned on or off to immediately change a current path to the LDs, thus responding to current at a higher speed (for example, see Patent Document 1).
In addition, there is also devised a drive circuit, that forcibly attenuates the output current of a constant current source circuit by causing a resistor to consume the output current to respond to the current at a higher speed (for example, see Patent Documents 2 and 3).